There is a definite need for easily-controllable power-driven wheel chairs for use by non-ambulatory patients. At the present time most of the available power-driven wheel chairs use a joy-stick type of control wherein a single lever is employed to correspondingly control the power drive means of the wheelchair. It has been found that with such a type of control the response and maneuverability of the wheel chair are unsatisfactory, especially in close quarters, due to insufficient sensitivity of the control system and inflexibility of the interface arrangements provided between the joy-stick, or equivalent control element, and the driving structures of the system.
In the previously issued U.S. Pat. No. 4,050,533 to Woodrow Seamone, it is proposed to employ an angular-position transducer incorporated in the coupling system between a hand rim element and a driving wheel, the hand rim element being resiliently coupled to the driving wheel. The transducer is in the form of a potentiometer adjusted in accordance with the amount of manual torque applied to the hand rim element. Upon sensing a change in resistance of the transducer caused by said torque an output is provided causing a desired change in the rotational motion of the driving wheel. In practice it has been found that a motorized wheel chair using this system is very jerky and uneven in operation because when the hand rim element is rotated it works against the torque of the motor until the transducer becomes effective, and because it is difficult to establish the desired new value of resistance adjustment of the potentiometer within a reasonably short time period. In other words, it is not possible to quickly set the transducer to its desired new-resistance position corresponding to that required for the desired new control signal value. Therefore, using merely a change of angular position of the hand rim element as the controlling factor does not appear to be a practical method of providing the required type of wheel chair control. Furthermore, this proposed system requires the patient to employ considerable muscular effort, and many patients do not possess the required strength to exert this effort.